here - Australian College of Veterinary Scientists

How I treat: equine
pemphigus foliaceus
Ralf Mueller
Pemphigus foliaceus (PF) is an autoimmune disease, directed against desmosomes in
the stratified squamous epithelium, leading to the loss of intracellular cohesion,
acantholysis and blister formation within the epidermis (Halliwell 1979, Laing and
others 1992, Scott and Miller 2003). It is the most common equine autoimmune
skin disease (Scott and others 1987, Von Tscharner and others 2000). The first
clinical article of pemphigus foliaceus in the horse was published by Barnick and
Gutzeit in 1891. In 1981, the first histopathologic and immunopathologic
documentation of equine PF in a horse was reported (Johnson and others 1981).
The reported age in recent publications varied from 2 months (Laing and others
1992) to 25.5 years (Zabel and others 2005). Most authors do not report breed, sex
predilection or seasonality (Scott and others 1983, Pascal and others 1995, Von
Tscharner and others 2000, Zabel and others 2005). Appaloosas were over
represented in one study (Scott 1989).
A retrospective study of 20 cases of equine pemphigus foliaceus reported an
increased prevalence of disease between September and February (Vandanebeele and
others 2004). Another recent retrospective study was not able to duplicate these
findings (Zabel and others 2005). Scott (1989) and White (1992) reported a
deterioration of disease in warm, humid, and sunny weather. Two horses (13%) in a
recent case series showed evidence of seasonal disease deterioration. One of these
horses, a Warmblood, did not show clinical signs during winter and deteriorated
every summer when it was brought on a high altitude pasture. After the horse was
kept in the valley permanently, no more clinical signs were noted (Zabel and others,
2005). Environmental factors such as increased exposure to ultraviolet light may
have been involved in the pathogenesis. The second horse was a research pony,
which showed worsening of clinical signs in summer and also related to stress
(anaesthesia, handling). Pemphigus foliaceus may be triggered by various factors
such as stress, drug administration, systemic disease or Culicoides hypersensitivity
(White 1992, Von Tscharner and others 2000), and the disease may wax and wane
(Fadok 1995). Von Tscharner and others (2000) describe hereditary as well as
infectious or environmental factors predisposing horses to pemphigus foliaceus, as
the disease has been noted in unrelated horses living in the same area. The head and
lower extremities have been reported as commonly affected sites (Von Tscharner
and others 2000, Scott and Miller 2003). In a report of 8 horses with pemphigus
foliaceus, a site predilection for the ventrum was found (Scott 1983). The disease
ACVSC Proceedings Dermatology Chapter Science Week 2005 95